This invention relates to a fault current limiting device, in which in a power circuit, short-circuit current or over-load current at the time of trouble is limited to a predetermined value thereby to reduce a mechanical damage caused by an electromagnetic force and a thermal damage caused by Joule heat, and prevent a secondary disaster resulting from these damages.
As apparatus for limiting short-circuit current at the time of trouble, there have heretofore been existed a power fuse and a disconnecting switch connected in series therewith.
This power fuse has a silver element, and the silver element becomes fused every current limiting operation. Therefore, the power fuse cannot be used repeatedly and need be replaced.
Further, as prior arts which overcome the above-described disadvantage, there are self-restoration type current limiters which use, as a current limiting material, mercury which is a metal having a low melting point (for example, Japanese Patent Publication No. 10643/1962), or alkaline metal (for example, Japanese Patent Publication No. 25432/1971), and a disconnecting switch or a circuit breaker connected in series therewith.
In the above-described self-restoration type current limiter using a low melting point metal, the low melting point metal is vaporized by the self Joule heat in the short-circuit current and changed into a plasma having a high temperature and high atmospheric pressure to produce a current limiting function. Therefore, a high pressure resisting vessel having an insulating portion becomes necessary, giving rise to a problem to a higher voltage.
Moreover, the low melting point metal material used includes those which adversely affect on the human body and have a strong reaction property, which has to be handled with care.
On the other hand, with an increase in power demand, rated current which is always normal load current also increases. Therefore, in the case of the aforementioned conventional fuse, if a design is made with rated current increased, there poses a disadvantage in that the current limiting function is deteriorated.
In view of the foregoing, normally, in the current limiter device, measures are taken as mentioned below so as not to lower the current limiting function.
That is, a load current carrying portion is separated from a current limiting portion, the load current carrying portion using a contact which is opened and closed rapidly. A load current carrying conductor is fused quickly by an explosive.
Alternatively, there is a method in which a load current carrying portion and a current limiting portion are integrally formed, and cooling fins are separately disposed or cooling water is circulated in order to suppress heat-generation caused by energization (Unexamined Publication Japanese Patent Application No. 134354/1979).